1. Field of the Invention
This disclosure relates to the field of electronic cables. In particular, to high speed cables for the transfer of digital information. Specifically, the cables discussed herein are multimedia cables which are more commonly called High Definition Multimedia Interface (HDMI) cables based upon the transmission standard commonly used across them. Based on their size, embodiments discussed herein could be described as miniature HDMI cables.
2. Description of Related Art
The field of home entertainment is growing exponentially. On the video front, black and white analog signals were state of the art 100 years ago. Now high-definition color is becoming the norm. Further, reliance on broadcast signals has been replaced with digital cable, Blu-Ray™ video sources, and digital recorders. Today's video screens can reproduce vast color palates in incredible resolution. Further, they generally have much larger (and differently proportioned) screens while still taking up less space.
Along with improvements to the video display of a home entertainment system, there have been major changes and improvements to audio reproduction. Audio today can also be stored and transferred digitally in conjunction with associated video or on its own. Further, no longer is there only a single speaker confined to being placed at the screen. Audio is provided in a multitude of channels to immerse the viewer into a program as never before possible.
Along with these improvements in sound and video reproduction, the rise of the Internet and computer storage of data has also created new ways to obtain entertainment. Digital storage and transmission of entertainment programming allows for a user to obtain copies of a particular entertainment program which can be played a near limitless number of times without degradation and that can be freely transferred between different pieces of equipment and watched “on-demand”.
With all this new functionality, however, comes the requirement to be able to transfer the data between an increasingly large number of different devices. While 20 years ago a television was a self contained device supplying audio, video, and content, today, the demand for better sources and reproduction has led to the average home theatre comprising a couple of core devices and a multitude of different peripherals. Transferring the data between these different devices has resulted in many entertainment systems having a rat's nest of cables of different standards and quality.
There are a lot of standards, and therefore also a lot of cables, that are used for the transmission of audio and video data. Component Video, S-Video, Fiber Optic, and others are all technologies which have their good and bad points. One of the principle concerns with much of the technology, however, is the proliferation of cables and the need to have a large number of physical cables to connect components. Further, a setup is often only as good as its weakest link.
In order to simplify the cable issue, the High Definition Multimedia Interface (HDMI) standard was previously proposed. This standard provides for a fully digital transmission of audio, video, and data across cables designed to use the standard. These HDMI cables are designed to meet the requirements and therefore provide conductors to carry three audio channels and three video channels (corresponding to the three components of a color signal) and a number of other supporting signals including those that can allow for devices to exchange instructions (consumer electronics channel (CEC)), hot plug detect for determining if components are added or removed, and the Display Data Channel (DDC) for encryption and related device information. Newer standards (HDMI 1.4) also include Ethernet data and audio return channels (HEAC). The standards of HDMI, along with how the cables are terminated at an HDMI jack are publicly available at www.hdmi.org, the entire disclosure of which is herein incorporated by reference.
An HDMI cable will need to include at least eighteen separate conductors to carry all the signals required under the current (version 1.3) HDMI standard. An embodiment of such a cable (900) is shown in FIG. 1. Twelve of the conductors are individually jacketed (forming cable cores indicated by the hollow circles of FIG. 1) and arranged into four twisted pair groups (with an unjacketed ground (represented by the shaded circles) each) (901), (903), (905), and (907) to carry the three channels of audio and video and a clock signal. Each twisted pair group then includes a dedicated jacket (991), (993), (995) and (997). Two conductors (one core and an unjacketed ground) form the power and general ground (911) while 4 remaining cores serve as the special channels. Specifically the DDC (which uses two cores) (921), CEC (923), and hot plug detect (925) along with an unused core (927) reserved for use by a future standard. Which of the specific cores (923), (925) and (927) is used for which purpose can change based on how the manufacturer chooses to connect the cores (923), (925), and (927).
The standard HDMI cable therefore comprises four component twisted-pair cables (each with its own shielding) (901), (903), (905), and (907), a power cable with ground (911), and specialty cores (921), (923), (925) and (927). This entire bundle is then placed inside a MYLAR (polyester film or plastic sheet) tape (952), wire braid shield (954), and insulative jacket (956) to form a representative HDMI cable.
While this arrangement provides for good signal quality and a simplified connection, it does provide some problems. Firstly, the use of twisted pair cables (901), (903), (905) and (907) requires additional space to accommodate the twisting as well as the inclusion of individual shielding (991), (993), (995) and (997) for each of the twisted pairs (901), (903), (905) and (907). This can make the cable (900) more bulky than necessary and can result in it being unsuitable for applications where a small cable may be necessary (for example in internal wiring or in portable devices).
Further the HDMI standard which utilizes parallel transmission can result in crosstalk between twisted pairs (901), (903), (905) and (907). Thus, as speed has to increase, and as cable length increases, wire gauge in the cores generally has to increase or else there can be signal degradation. As the signal is digital, instead of analog, signal degradation can result in parts of the signal being lost which in turn can result in a massively degraded signal quality. As the HDMI standard is real time (as opposed to most standard data transmission such as in Ethernet connections), there are also enormous problems with longer cable runs and reliable HDMI transmission has generally been limited to only a few feet.
In many cases this is acceptable as the distance between components in a home theatre may be well within these distances. For some applications, however, the length limitation can be significant. When particularly small diameter cables are needed (such as with portable devices or connections internal to devices where space is a premium) the traditional HDMI cable may simply be unable to provide reliable performance.
For the above and other reasons known to those of ordinary skill in the art, described herein is a multimedia cable designed for use with HDMI standards (such as, but not limited to, HDMI 1.3 and 1.4) which provides for a coaxial arrangement of internal conductors doing away with the traditional twisted pair construction while still maintaining signal quality.